1. Field of the Invention
The present invention relates to an image pickup apparatus which is used for a digital still camera, a video camera and the like, and an image pickup system which uses the image pickup apparatus.
2. Description of the Related Art
In a digital still camera, an image pickup device having 10,000,000 pixels is used recently. Such an aspect is a result of pursuing image quality which is equivalent to that of a silver halide camera, and the digital still camera of this type is mainly used to handle still images. On the other hand, the number of pixels necessary to obtain moving images corresponding to a Full High Definition Television system is about 2,000,000.
For example, if the image pickup device having the 10,000,000 pixels is used to handle moving images, reading speed as much as five times of reading speed of the case of 2,000,000 pixels is necessary, and thus power consumption remarkably increases. In this case, there is a problem that noises increase due to the increase of the power consumption. Further, there is a problem of increasing costs due to the increase of the capacity of a memory to be used for image processing.
To solve the above-described problems, for example, a specific image pickup apparatus is disclosed in Japanese Patent Application Laid-Open No. 2000-341699. That is, in this apparatus, since signals of plural pixels are handled by a common amplifier, electrical charges of these signals are added and read at the input node of the common amplifier.
However, in the image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-341699, the constitution for driving the pixels becomes complicated. Further, according to such complexity, the number of wirings necessary to drive the pixels increases, and thus an aperture ratio decreases. For these reasons, since the circuit constitution for driving the pixels increases in scale, the costs for this constitution increase. Further, since the sensitivity of the image pickup apparatus decreases, excellent image quality cannot be obtained.
Under such circumstances, for example, Japanese Patent Application Laid-Open No. 2006-073733 discloses an image pickup apparatus which can solve such problems. That is, in this apparatus, since a common amplifier is used for pixels of four rows and one column, it is unnecessary to increase wirings to be used for driving these pixels, and electrical charges of signals can be added to others on the pixels.
Further, U.S. Pat. No. 6,734,414 discloses a technique of connecting one gate line to a part of pixels on a certain line and of also connecting this gate line to a part of pixels on a line adjacent to the certain line, thereby dispersing noises correlating with the lines.
In the image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-073733, the addition of the signals on the pixels is performed only in the vertical direction. However, since image information of each color after the addition comes not to have spatially equal intervals according to the arrangement of a color filter, there is a problem that resolution deteriorates. For this reason, it is required to add the pixel signals in a diagonal direction. That is, in the image pickup apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-073733, to add the signals of the pixels adjacent in the diagonal direction (that is, the diagonally adjacent pixels), it is necessary to additionally provide a circuit such as a line memory for holding the signals. Furthermore, since the pixels are generally scanned in units of row or in units of column, there is a problem that both the circuit constitution and the driving method become complicated in order to add the signals in the diagonal direction.
Furthermore, U.S. Pat. No. 6,734,414 does not disclose any addition of signals supplied from diagonally adjacent pixels.